ELECTRON-PARAMAGNETIC RESONANCE SPECTROSCOPY OF SPIN-LABELED CUTICLE OF CENTRUROIDES-SCULPTURATUS (SCORPIONES, BUTHIDAE) - CORRELATION WITH THERMAL EFFECTS ON CUTICULAR PERMEABILITY

Cuticular phase transitions and molecular dynamics have been studied in the buthid scorpion Centruroides sculpturatus using the techniques of thermogravimetric analysis (TGA) and electron paramagnetic resonance (EPR). TGA studies of the cuticular permeability reveal discontinuous changes in thermal dependence of transcuticular water loss rates (transitions). The first transition occurs between 30-40 C and results in a small increase in water loss rate, whereas the second transition begins near 55 C and is accompanied by a large increase in water loss rate. EPR spectra of spin-labelled cuticle indicate that the epicuticular lipids are very mobile at ambient temperature, with the translational diffusion coefficient being about 5 × 10-6 cm2 sec at 22 C. and that the low-temperature transition is associated with an increase in mobility of the hydrocarbon chains of the epicuticular lipids. The high-temperature transition probably results from melting of the epicuticular lipids. The results of this study are discussed with reference to current models of the structure of the arthropod cuticle. © 1979.